1. Field of the Invention
The present invention relates to a fuel injector intended for use in an internal combustion engine, especially in a Diesel engine. More particularly, it relates to an accumulator nozzle type fuel injector and a fuel injection system provided with the same.
2. Description of the Related Art
In the conventional accumulator nozzle type fuel injector, the pressure of fuel supplied from a fuel source does not act on the needle valve in the valve-closing direction but acts only in the valve-opening direction, with the force of a spring acting in the valve-closing direction. In addition, the needle valve is so arranged that when the supply of fuel is stopped, the valve opens to allow fuel to be injected from the nozzle hole so that the fuel pressure within the accumulator is reduced, and thus the needle valve can close, terminating the fuel injection.
In the conventional fuel injector having the above construction, the valve-closing pressure depends upon the force (i.e., size) of the spring, and thus the size of the fuel injector is necessarily limited. Accordingly, since the needle valve can be opened under a relatively low pressure, a sufficient fuel injection pressure cannot be obtained. In other words, fuel atomization is limited and it is difficult to further improve the engine performance. Also, the conventional fuel injector is so constructed that the needle valve is opened when the fuel supply is stopped, and is closed as the fuel pressure within the accumulator decreases; therefore, the operating noise is loud, since the fuel injection time is extremely short and thus the needle is opened and closed rapidly and abruptly.
To minimize this noise, the fuel injection rate of the internal combustion engine should be controlled in accordance with the running conditions of the engine. This fuel injection rate control must be such that the injection rate is low in the low-speed, low-load domain of the engine and is high in the high-speed, high-load domain.